I wish to learn to adjustments, hue, saturation etc

Wow... I'm watching until now one video just to understand in general about histogram. I'm not fully convinced of how to use histogram, but in general I'm understanding that it's the Histogram that says me if there's too much reds or if there's too much blues, or if there's too much dark or light.... it seems what it could help me a lot to regolate the adjustments ! So it's not something that I have to do by myself, (or at least, if I want properly a much blue image for some reason, it's ok), but when one just want to regolate the colors, hightlights in a balanced way, without creating 'particular' effects, but just balance the correct tones in harmony between each others, it seems histogram can be really fundamental tool... surely this is a good step to start to learn much more about it!  But I'm a bit confused about this video i'm watching, I need to study about this...very very interesting.. wow.... I'm entusiast right now! For me it's something totally new! 

Thank you so much for all the tips! 
Also, very interesting methods to use. 
And I'm going to find some informations about "histogram". I'm curious about it, because I 've never understood what is it exactly. I see all those colors (a little like when I use curves), but an histogram I see many colors... Im very interested to understand what is this 'mysterious' tool.... !

I doubt you will find a set formula as every starting image is different, and every photographer will develop their own approach.

Find some reference images that you do like and open them. Then start with your own image and work with adjustment layers and masks to hone in on a 'look' . Make global adjustments before you use masks to make local corrections.

All the way through, switch back and forth between your image and the reference images. That way you are always 'recalibrating your eye and brain' to ensure you are progressing toward that look and not away from it.

Use the histogram to ensure you are not going to light or too dark in comparison to your references.

Finally, but importantly, get a calibration device, and calibrate and profile your monitor so you are not compensating for defects in the display system. Whilst viewing the references on the same monitor will go someway to negating the need for that, if you are serious about your image quality it is important to know you are viewing the results of your adjustments correctly.

Dave

Thanks for all the tips!

Yes, to experiment it's one part, but I think it miss something yet.
Yesterday I casually found an interview from someone that work on Photoshop for a lot of years, and he says exactly what I feel:

https://www.juliaannagospodarou.com/fine-art-photography-principles/

 Me too,  I feel like I'm working 'randomly', I experiment values of brightness, contrast, hue, saturations, but without follow rules, it come out always a bad end result, especially because I don't need just one adjustment layer but many. So if there's not a certain 'armony' and 'consciouness' when I add layers adjustments between them, in prevision also of the other layers, I will always do a wrong work, even if I experiment for a long time".
Here what I feel from this artist of photography's interview::

"When you don’t cultivate a talent you have, it is like expecting to get every time a jackpot only because you had good cards once. But that doesn’t happen. I’ve seen this happening many times looking at photographs around me that are created by artists who have a talent for composition but who at times cannot meet their potential because they work randomly."

From my experience in my architecture and artistic background, in drawing and photography, and taking into consideration all the information and knowledge I have acquired over almost 30 years working in art-related fields, plus the rich experience of working with photography students, I can tell you that the best compositions come from training your eye, knowing the rules and becoming confident enough to know when to apply and when not to apply a rule, when to break the known rules and create your own.

You cannot be a total artist if you ignore composition because composition is the science of a harmonious communication with the viewer. (..)   

One can experiment, but needs to know the rules, I need to understand how I have to use certain colors, vibrances, I don't know, I wish to find a book that teach all these things about Painting.
I've found a book , I wonder if is good for what I 'm trying to learn?

I would second what Leslie said. There really are no hard fast rules, but more what you like, what feel or mood you want to impart. Playing with the tools, especially curves will help you know how to use them to achieve the look you want. Also the quicker you can be in correcting an image, especially color, the better. Your eye adapts quickly to the changes you make to an image, and it's real easy to go overboard with corrections. Always best to compare it with the original, and to walk away from it, for a bit and look at it later. If you have a lot of images, after you correct them, cycle through them and see if any stick out due to bad color. Years ago, when I was working as a color corrector for a pro lab in their portrait department, all the color corrector were invited to a gallery showing, in which our company printed the images. We were all aghast at how bad the color between the different images. It's so easy to go astray without a reference. 

For example, there's actually books specific and professional , that teach how to set colors and create good colors like in this image:

Books about fine arts with Photoshop painting. But not books that teach how to paint, but how to adjust colors, hue, saturations ,tones, how to use shadows, highlights , and not giving numbers to copy , but to master the rules to behind that, so that one know what is doing!

😄